/*
 * Copyright 2002-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.resource;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.core.OrderComparator;
import org.springframework.util.AntPathMatcher;
import org.springframework.util.Assert;
import org.springframework.util.PathMatcher;
import org.springframework.web.servlet.HandlerMapping;
import org.springframework.web.servlet.handler.SimpleUrlHandlerMapping;
import org.springframework.web.util.UrlPathHelper;

import javax.servlet.http.HttpServletRequest;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;


/**
 * A central component to use to obtain the public URL path that clients should
 * use to access a static resource.
 *
 * <p>This class is aware of Spring MVC handler mappings used to serve static
 * resources and uses the {@code ResourceResolver} chains of the configured
 * {@code ResourceHttpRequestHandler}s to make its decisions.
 *
 * @author Rossen Stoyanchev
 * @since 4.1
 */
public class ResourceUrlProvider implements ApplicationListener<ContextRefreshedEvent> {

    protected final Log logger = LogFactory.getLog(getClass());

    private UrlPathHelper pathHelper = new UrlPathHelper();

    private PathMatcher pathMatcher = new AntPathMatcher();

    private final Map<String, ResourceHttpRequestHandler> handlerMap = new HashMap<String, ResourceHttpRequestHandler>();

    private boolean autodetect = true;


    /**
     * Configure a {@code UrlPathHelper} to use in
     * {@link #getForRequestUrl(javax.servlet.http.HttpServletRequest, String)}
     * in order to derive the lookup path for a target request URL path.
     */
    public void setUrlPathHelper(UrlPathHelper pathHelper) {
        this.pathHelper = pathHelper;
    }

    /**
     * @return the configured {@code UrlPathHelper}.
     */
    public UrlPathHelper getPathHelper() {
        return this.pathHelper;
    }

    /**
     * Configure a {@code PathMatcher} to use when comparing target lookup path
     * against resource mappings.
     */
    public void setPathMatcher(PathMatcher pathMatcher) {
        this.pathMatcher = pathMatcher;
    }

    /**
     * @return the configured {@code PathMatcher}.
     */
    public PathMatcher getPathMatcher() {
        return this.pathMatcher;
    }

    /**
     * Manually configure the resource mappings.
     *
     * <p><strong>Note:</strong> by default resource mappings are auto-detected
     * from the Spring {@code ApplicationContext}. However if this property is
     * used, the auto-detection is turned off.
     */
    public void setHandlerMap(Map<String, ResourceHttpRequestHandler> handlerMap) {
        if (handlerMap != null) {
            this.handlerMap.clear();
            this.handlerMap.putAll(handlerMap);
            this.autodetect = false;
        }
    }

    /**
     * @return the resource mappings, either manually configured or auto-detected
     * when the Spring {@code ApplicationContext} is refreshed.
     */
    public Map<String, ResourceHttpRequestHandler> getHandlerMap() {
        return this.handlerMap;
    }

    /**
     * @return {@code false} if resource mappings were manually configured,
     * {@code true} otherwise.
     */
    public boolean isAutodetect() {
        return this.autodetect;
    }

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        if (isAutodetect()) {
            this.handlerMap.clear();
            detectResourceHandlers(event.getApplicationContext());
            if (this.handlerMap.isEmpty() && logger.isDebugEnabled()) {
                logger.debug("No resource handling mappings found");
            }
        }
    }

    protected void detectResourceHandlers(ApplicationContext appContext) {

        logger.debug("Looking for resource handler mappings");

        Map<String, SimpleUrlHandlerMapping> map = appContext.getBeansOfType(SimpleUrlHandlerMapping.class);
        List<SimpleUrlHandlerMapping> handlerMappings = new ArrayList<SimpleUrlHandlerMapping>(map.values());
        Collections.sort(handlerMappings, new OrderComparator());

        for (SimpleUrlHandlerMapping hm : handlerMappings) {
            for (String pattern : hm.getUrlMap().keySet()) {
                Object handler = hm.getUrlMap().get(pattern);
                if(handler instanceof String) {
                    handler = hm.getApplicationContext().getBean((String)handler);
                }
                if (handler instanceof ResourceHttpRequestHandler) {
                    ResourceHttpRequestHandler resourceHandler = (ResourceHttpRequestHandler) handler;
                    if (logger.isDebugEnabled()) {
                        logger.debug("Found resource handler mapping: URL pattern=\"" + pattern + "\", " +
                                "locations=" + resourceHandler.getLocations() + ", " +
                                "resolvers=" + resourceHandler.getResourceResolvers());
                    }
                    this.handlerMap.put(pattern, resourceHandler);
                }
            }
        }
    }


    /**
     * A variation on {@link #getForLookupPath(String)} that accepts a full request
     * URL path (i.e. including context and servlet path) and returns the full request
     * URL path to expose for public use.
     *
     * @param request the current request
     * @param requestUrl the request URL path to resolve
     * @return the resolved public URL path or {@code null} if unresolved
     */
    public final String getForRequestUrl(HttpServletRequest request, String requestUrl) {
        if (logger.isTraceEnabled()) {
            logger.trace("Getting resource URL for requestURL=" + requestUrl);
        }

        String pathWithinMapping = (String) request.getAttribute(HandlerMapping.PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE);
        if (pathWithinMapping == null) {
            logger.trace("Request attribute with lookup path not found, calculating instead.");
            pathWithinMapping = getPathHelper().getLookupPathForRequest(request);
        }

        int index = getPathHelper().getRequestUri(request).indexOf(pathWithinMapping);
        Assert.state(index > 0 && index < requestUrl.length(), "Failed to determine lookup path: " + requestUrl);

        String prefix = requestUrl.substring(0, index);
        String lookupPath = requestUrl.substring(index);
        String resolvedPath = getForLookupPath(lookupPath);

        return (resolvedPath != null) ? prefix + resolvedPath : null;
    }

    /**
     * Compare the given path against configured resource handler mappings and
     * if a match is found use the {@code ResourceResolver} chain of the matched
     * {@code ResourceHttpRequestHandler} to resolve the URL path to expose for
     * public use.
     *
     * <p>It is expected the given path is what Spring MVC would use for request
     * mapping purposes, i.e. excluding context and servlet path portions.
     *
     * @param lookupPath the lookup path to check
     * @return the resolved public URL path or {@code null} if unresolved
     */
    public final String getForLookupPath(String lookupPath) {
        if (logger.isTraceEnabled()) {
            logger.trace("Getting resource URL for lookupPath=" + lookupPath);
        }
        for (String pattern : this.handlerMap.keySet()) {
            if (!getPathMatcher().match(pattern, lookupPath)) {
                continue;
            }
            String pathWithinMapping = getPathMatcher().extractPathWithinPattern(pattern, lookupPath);
            String pathMapping = lookupPath.substring(0, lookupPath.indexOf(pathWithinMapping));
            if (logger.isTraceEnabled()) {
                logger.trace("Invoking ResourceResolverChain for URL pattern=\"" + pattern + "\"");
            }
            ResourceHttpRequestHandler handler = this.handlerMap.get(pattern);
            ResourceResolverChain chain = new DefaultResourceResolverChain(handler.getResourceResolvers());
            String resolved = chain.resolveUrlPath(pathWithinMapping, handler.getLocations());
            if (resolved == null) {
                throw new IllegalStateException("Failed to get public resource URL path for " + pathWithinMapping);
            }
            if (logger.isTraceEnabled()) {
                logger.trace("Resolved public resource URL path=\"" + resolved + "\"");
            }
            return pathMapping + resolved;
        }
        logger.debug("No matching resource mapping");
        return null;
    }

}
